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  2. Equivalent radius - Wikipedia

    en.wikipedia.org/wiki/Equivalent_radius

    US hat size is the circumference of the head, measured in inches, divided by pi, rounded to the nearest 1/8 inch. This corresponds to the 1D mean diameter. [1] Diameter at breast height is the circumference of tree trunk, measured at height of 4.5 feet, divided by pi. This corresponds to the 1D mean diameter.

  3. Circular mil - Wikipedia

    en.wikipedia.org/wiki/Circular_mil

    The area in circular mils, A, of a circle with a diameter of d mils, is given by the formula: {} = {}. In Canada and the United States, the Canadian Electrical Code (CEC) and the National Electrical Code (NEC), respectively, use the circular mil to define wire sizes larger than 0000 AWG .

  4. Area of a circle - Wikipedia

    en.wikipedia.org/wiki/Area_of_a_circle

    Here, the Greek letter π represents the constant ratio of the circumference of any circle to its diameter, approximately equal to 3.14159. One method of deriving this formula, which originated with Archimedes, involves viewing the circle as the limit of a sequence of regular polygons with an increasing number of sides

  5. Circle - Wikipedia

    en.wikipedia.org/wiki/Circle

    The tangent line through a point P on the circle is perpendicular to the diameter passing through P. If P = (x 1, y 1) and the circle has centre (a, b) and radius r, then the tangent line is perpendicular to the line from (a, b) to (x 1, y 1), so it has the form (x 1 − a)x + (y 1 – b)y = c.

  6. Zeiss formula - Wikipedia

    en.wikipedia.org/wiki/Zeiss_formula

    The number 1/1730 derives from a circle of confusion diameter of 0.025 mm on a full-frame 35 mm film format, with diagonal size about 43.25 mm (43.25/0.025 is 1730). The CoC size of 0.025 mm for this format appears in Jacobson's Photographic Lenses Tutorial, [ 1 ] and the 1730 in his 1996 Photographic Lenses FAQ. [ 2 ]

  7. Sagitta (geometry) - Wikipedia

    en.wikipedia.org/wiki/Sagitta_(geometry)

    In geometry, the sagitta (sometimes abbreviated as sag [1]) of a circular arc is the distance from the midpoint of the arc to the midpoint of its chord. [2] It is used extensively in architecture when calculating the arc necessary to span a certain height and distance and also in optics where it is used to find the depth of a spherical mirror ...

  8. Machin-like formula - Wikipedia

    en.wikipedia.org/wiki/Machin-like_formula

    In mathematics, Machin-like formulas are a popular technique for computing π (the ratio of the circumference to the diameter of a circle) to a large number of digits.They are generalizations of John Machin's formula from 1706:

  9. Gauss circle problem - Wikipedia

    en.wikipedia.org/wiki/Gauss_circle_problem

    Gauss's circle problem asks how many points there are inside this circle of the form (,) where and are both integers. Since the equation of this circle is given in Cartesian coordinates by x 2 + y 2 = r 2 {\displaystyle x^{2}+y^{2}=r^{2}} , the question is equivalently asking how many pairs of integers m and n there are such that